Normally, the first thing you do after loading MultiWii EZ-GUI is use the MW Connect button on the top of the screen (in the actionbar) to get connected to your MultiWii-based flight controller.
When not connected all possible buttons are visible. After connection functions not supported by your flight controller will be hidden.
However, you can explore the rest of MultiWii EZ-GUI without connecting first – and you may have to do that if you need to change Bluetooth or other settings in the Config menu.
If you are using Bluetooth and your phone’s Bluetooth is off when you start the app, MultiWii EZ-GUI will automatically enable Bluetooth when the app loads, and disable it when you exit.